PATTERNS IN DISTRIBUTION AND ABUNDANCE OF A 

 NONCOEVOLVED ASSEMBLAGE OF ESTUARINE FISHES IN CALIFORNIA 



Peter B. Moyle, 1 Robert A. Daniels, 2 Bruce Herbold, 1 

 and Donald M. Baltz 3 



ABSTRACT 



The patterns of distribution and abundance of the fishes of Suisun Marsh, a portion of the Sacramento- 

 San Joaquin estuary in central California, were studied over a 54-month period. Tbtal fish abundance 

 in the marsh exhibited strong seasonality; numbers and biomass were lowest in winter and spring and 

 highest in late summer. Freshwater inflow was highest in the winter and lowest in late summer, when 

 salinities and temperatures were highest. Twenty-one species were collected on a regular basis; the 10 

 most abundant were Morone saxatilis, Pogonichthys macrolepidotus, Gasterosteus aculeatus, Hysterocarpus 

 traski, Cottus asper, Spirinchus thaleichthys, Acanthogobius fl.avimanus, Catostomus occidentalis, Lep- 

 tocottus armatus, and Platichthys stellatus. Another 21 species occurred in small numbers on an irregular 

 basis. Twenty of the 42 species had been introduced to California since 1879. Of the 21 common species, 

 14 were residents, 4 were winter seasonals, and 3 were spring/summer seasonals. The resident species 

 fell into two groups: a group of native species that were concentrated in small dead-end sloughs and a 

 group of native and introduced species that were most abundant in the larger sloughs. The seasonal species 

 were also a mixture of native and introduced species. Tbtal fish abundance and species diversity declined 

 through the study period, which seemed to be related to strong year classes of some species early in 

 the study and the prevalance of freshwater conditions late in the study. The structure of the fish assemblage 

 was fairly consistent over the study period but changes are expected in the near future The structure 

 of the Suisun Marsh fish assemblage was similar to that found in other river-dominated estuaries, despite 

 the mixture of native and introduced species. 



The Sacramento-San Joaquin Estuary system is the 

 largest estuary on the west coast of North America. 

 It has been highly modified by surrounding urban, 

 industrial, and agricultural development and by ex- 

 tensive diversion and pollution of the freshwater that 

 flows into it (Conomos 1979). It supports a diverse 

 fish fauna of native and introduced species, but most 

 previous studies have concentrated on species impor- 

 tant to sport and commercial fisheries, especially 

 striped bass, Morone saxatilis, and, to a much lesser 

 extent, white sturgeon, Acipenser transmontanus; 

 chinook salmon, Oncorhynchus tshawytscha; Ameri- 

 can shad, Alosa sapidissima; and white catfish, Icta- 

 lurus catus (Skinner 1972; Moyle 1976). Studies of 

 other species have been few (Ganssle 1966; Turner 

 and Kelley 1966; Baltz and Moyle 1982; Stevens and 

 Miller 1983; Daniels and Moyle 1983), and there have 

 been no community-level analyses equivalent to those 

 conducted on estuarine fish communities in other 



'Wildlife and Fisheries Biology, University of California, Davis, 

 CA 95616. 



z Wildlife and Fisheries Biology, University of California, Davis, 

 CA; present address: Biological Survey, New York State Museum, 

 Albany, NY 12230. 



3 Wildlife and Fisheries Biology, University of California, Davis, 

 CA; present address: Coastal Fisheries Institute, Louisiana State 

 University, Baton Rouge, LA 70803. 



parts of the world (e.g., Dahlberg and Odum 1970; 

 Livingston 1976; Sheridan and Livingston 1979; 

 Meeter et al. 1979; Blaber and Blaber 1980; Quinn 

 1980; Thorman 1982). The fish assemblage of the 

 Sacramento-San Joaquin Estuary system is unusual 

 because few of its component species are likely to 

 have evolved together; it is composed of a mixture 

 of introduced and native freshwater, estuarine, and 

 euryhaline marine species (Table 1). The introduced 

 species come from a number of geographic areas, 

 while most of the native species have their centers 

 of abundance in either the rivers upstream or the 

 saltwater bays downstream from the estuary. There 

 are no really comparable estuaries on the Califor- 

 nia coast, although some of the much smaller and 

 more saline estuaries south of the Sacramento-San 

 Joaquin Estuary do have fish assemblages composed 

 in part of introduced species (Allen 1982). 



We began in January 1979 systematic sampling 

 of the fishes in Suisun Marsh on a monthly basis. 

 Suisun Marsh was chosen as a study site because of 

 its central location on the estuary, its proximity to 

 the University of California, Davis campus, and the 

 availability of earlier data from sporadic sampling 

 by the California Department of Fish and Game The 

 data indicated that the fish fauna was typical of the 



Manuscript accepted March 1985. 



FISHERY BULLETIN: VOL. 84, NO. 1, 1986. 



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